The present invention pertains to the field of roller screeds and more particularly pertains to powered roller screeds for screeding cementitious material.
Concrete structures are formed by pouring a cementitious material, such as cement and aggregate (referred to herein as concrete) into a form, or other container, and permitting the material to cure under proper conditions. In the case of a concrete pad, such as a floor, foundation, or roadway, concrete is poured onto a ground, or support, surface and contained by forms connected to, and rising above, the ground, or support, surface. The forms are longitudinal members arranged along a border of a desired location for the concrete pad to contain the viscous concrete and provide a guide for the concrete""s thickness and to level the top surface of the concrete.
After concrete is poured between forms, it is spread evenly between the forms. A screed is then used to remove excess concrete and level the top surface of the concrete so it is even with the forms. Often, several passes of a screed over the concrete is necessary to achieve the desired surface. Precision is required to conform to building codes and to perform quality work.
A very primitive screed, which is still useful on small jobs, is a simple straight edge such as a straight board. A board, long enough to span the forms, is laid on top of each form and thereafter pulled down the length of the forms by workers at each end of the board. This pushes forward excess concrete: excess concrete is concrete that is higher than the top surface of the forms. While quite suitable for small jobs, such a screed is impractical on large jobs because of the work required to move the excess concrete.
A more practical screed for larger jobs is disclosed in Mitchell, U.S. Pat. No. 4,142,816. Mitchell discloses a powered screed having a hydraulic motor to spin a tubular member while the screed is pulled along the forms by two workers, one each located on either side of the forms. As with most rotary screeds, the tubular member spins in a direction opposite a direction of travel of the screed. By spinning the tube, this screed provides a good surface to the concrete. However, substantial work is required to pull the screed along the forms. The hydraulic motor, spinning the tube, does not assist to propel the screed forward and the heavy concrete that builds up in front of the screed requires a large amount of force to move. In addition, workers located at each end of the Mitchell screed must keep the screed tube substantially perpendicular to the formsxe2x80x94frequently this is a difficult task because of uneven amounts of concrete from side-to-side and unequal strengths of the workers.
Larger, powered screeds are suitable for large, high-volume jobs. U.S. Pat. No. 5,456,549 discloses a powered rotary screed having a modular frame that spans across concrete-retaining forms to supports a strike tube and drive tubes. The frame provides rigidity and support so that the screed can span large distances between forms. The strike tube rotates opposite the direction of screed travel to screed the concrete and the drive tubes provide motive force to propel the screed. While very useful for large jobs, and jobs that are not constrained by space limitations, these larger screeds are difficult to use in areas surrounded by obstacles and are more difficult to transport than the smaller screed described above. Also, in the event the screed becomes mis-aligned with the forms, the screed must be manually re-aligned, such as by holding back a leading end of the screed so that the trailing end can catch up.
Accordingly, there is a need in the industry to provide a powered screed that can be easily operated, even in areas that are constrained by nearby obstacles, and conveniently transported and set up for use.
The present invention provides a frameless roller screed having a drive tube to assist the screed operators to move the screed along forms over freshly poured concrete. The present invention has no form-spanning supporting structure or frame, thereby providing a lightweight, maneuverable, and easily transported screed. In addition, by providing handles, arranged as levers, in combination with a single drive tube and strike tube, the handles can be easily manipulated to control the effect of the drive tube for easy operation.
Preferably, hydraulic motors drive the strike tube and the drive tube. The strike tube is the leading edge of the screed as the screed is powered along the forms and by rotating the strike tube the advantages of a rotary screed are achievedxe2x80x94i.e., a better surface on the concrete. The drive tube is powered to provide mechanical assistance to push excess concrete forward as the screed moves along the forms. By providing motive power to the screed of the present invention, the screed operators can concentrate on achieving a high-quality finish on the concrete.
Preferably, the present invention screed is maneuvered by handles located on opposite ends of the screed and arranged as levers. The handles are pivotally mounted to frame elements so that the handles may be pivoted to provide greater screed maneuverability. For example, the handles may be pivoted outward allowing the screed to be driven up to obstacles such as a vertical wall at the end of a concrete pad.
Further, the handles are coupled to the screed such that an operator can push a distal end of the handle downward, or raise the distal end upward, to lever the drive tube about the strike tube. Accordingly, pushing down on the handle tends to lift the drive tube off of the forms so that forward motion of the screed may be easily, and quickly, halted. Alternatively, lifting the handles places more of the screed""s weight on the drive tube and increases the drive tube""s pressure on the forms so that the drive tube can provide more motive force without slipping.
The roller tubes of the present invention are coupled together by plates located on distal ends of the screed. The screed has no frame that extends substantially over the concrete, or spans the forms. Preferably, at least one of the plates includes an anti-skew box structure that prevents the tubes from skewing relative to one another and relative to the plates.
Accordingly, the present invention provides a frameless, powered roller screed having motive force to drive the screed along forms and assist in the difficult task of screeding heavy concrete. In addition, the present invention provides handles that can lever the drive tube to provide substantial control over the motive force generated by the drive tube. Also, the handles are provided with pivotal connections to connecting plates for greater screed maneuverability. And, by providing no frame elements that extend across the forms, the screed of the present invention is relatively easier to transport and setup as compared to prior art screeds having drive tubes.